Conventionally, a metal foam has been known as a material similar to a cellular light structure. The metal foam is manufactured by producing bubbles inside a metal of liquid or semi-solid state (closed cell-type), or by casting the metal into a mold made of a foaming resin such as sponge (open cell-type). However, these metal foams have relatively poor mechanical properties such as strength and rigidity. In addition, due to its high manufacturing cost, it has not been used widely in practice, except for a special purpose such as in aerospace or aviation industries.
As a substitute material for the above mentioned metal foams, open cell-type light structures with periodic truss cells have been suggested. This open cell-type light structure is designed so as to have an optimum strength and rigidity through precise mathematical and mechanical analysis, and therefore it has good mechanical properties. A typical truss structure is exemplified by the Octet truss where regular tetrahedrons and regular octahedrons are combined (See R. Buckminster Fuller, 1961, U.S. Pat. No. 2,986,241). Each element of the truss forms an equilateral triangle and thus it is advantageous in terms of strength and rigidity. Recently, as a modification of the Octet truss, the Kagome truss has been reported (See S. Hyun, A. M. Karlsson, S. Torquato, A. G. Evans, 2003, Int. J. of Solids and Structures, Vol. 40, pp. 6989-6998).
Referring to FIG. 1, when the two-dimensional Octet truss 101 and the two-dimensional Kagome truss 102 are compared, a unit cell 102a of the Kagome truss 102 has an equilateral triangle and a regular hexagon mixed in each face, dissimilar to a unit cell 101a of the Octet truss 101.
FIGS. 2 and 3 show a single layer of the three-dimensional Octet truss 201 and the three-dimensional Kagome truss 202, respectively. Comparing a unit cell 201a of the three-dimensional Octet truss 201 with a unit cell 202a of the three-dimensional Kagome truss 202, one of the significant features of the three-dimensional Kagome truss 202 is that it has low anisotropic. Therefore, the structural materials or other materials based on the Kagome truss 202 have almost a uniform mechanical and electrical property regardless of its orientation.
Several processes have been used for manufacturing a truss-type cellular light structure. First, a truss structure is formed of a resin, and a metal is cast using the truss structure as a mold, i.e., investment casting (See S. Chiras, D. R. Mum, N. Wicks, A. G. Evans, J. W. Hutchinson, K. Dharmasena, H. N. G. Wadley, S. Fichter, 2002, International Journal of Solids and Structures, Vol. 39, pp. 4093-4115). Second, a metallic mesh is formed by punching periodic holes in a thin metal plate, and a truss layer is formed by bending the metallic mesh. Then, face sheets are bonded to the upper and lower portions of the truss layer as a core of a sandwich panel (See D. J. Sypeck and H. N. G. Wadley, 2002, Advanced Engineering Materials, Vol. 4, pp. 759-764). Here, in the case where a two-layered structure is to be fabricated, another truss intermediate layer is placed on the upper face sheet and another upper face sheet is positioned again thereon. By repeating the same procedure, multi-layered structure can be fabricated. In the third method, wire nets are first woven using two orientational wires perpendicular to each other, and then the wire nets are laminated and bonded (See D. J. Sypeck and H. G. N. Wadley, 2001, J. Mater, Res., Vol. 16, pp. 890-897).
As for the first method, its complicated manufacture process leads to a high manufacture cost. Only metals having a good castability can be applied and consequently it has limited applications. The resultant material tends to have casting defects and deficient strength. As for the second method, the process punching periodic holes in thin metal plate leads to loss of material. Moreover, even though there is no specific problem in manufacturing a sandwiched plate having a single-layered truss, the truss cores and face sheets must be laminated and bonded repeatedly so as to manufacture a multi-layered structure, thereby producing many bonding points which results in disadvantages in terms of bonding cost and strength.
As for the third method, basically the formed truss has no ideal regular tetrahedron or pyramid shape and thus has an inferior mechanical strength. Similar to the second method, lamination and bonding are must be involved for manufacturing a multi-layered structure and therefore disadvantageous in respect of bonding cost and strength.
FIG. 4 shows a light structure manufactured by the third method, which is formed by laminating wire nets. This method is known to be able to reduce the manufacturing cost, but wires of two orientations are woven like fabrics, and therefore it cannot provide an ideal structure having as good mechanical strength as in the above-described three-dimensional Octet truss 201 or the three-dimensional Kagome truss 202. Accordingly, it has disadvantages in terms of the cost and the strength, due to lots of portions to be bonded.
Meanwhile, a common fiber reinforced composite material is manufactured in the form of thin two-dimensional layer, which is laminated when a thick material is required.
However, in this case, due to delamination phenomenon between the layers, its strength tends to be deteriorated. In order to prevent the delamination, the fiber is woven into a three-dimensional structure from the beginning, and then a matrix such as resin, metal, or the like is combined with the structure. FIG. 5 shows a perspective view of the woven fibers in this three-dimensional fiber reinforced composite material. Instead of fibers, a material such as a metallic wire having a high stiffness can be woven into a three-dimensional cellular light structure as shown in FIG. 5. However, it also does not have the above-described ideal Octet or Kagome truss structure, and it has a decreased mechanical strength and more anisotropic material properties. Consequently, the composite material formed of the three-dimensional woven-fibers comes to have inferior mechanical properties.
In view of the aforementioned shortcomings, the inventors of the present invention have devised a three-dimensional cellular light structure which is manufactured in a uniform pattern similar to the ideal Kagome truss or Octet truss by intercrossing six-axial continuous wire groups at 60 degrees or 120 degrees of angles in a space, and a manufacturing method thereof, which is disclosed in Korean Patent Publication No. 10-2006-0095968 (hereinafter, earlier-filed invention).
The three-dimensional cellular light structure manufactured according to the earlier-filed invention has several advantages in that it has good mechanical properties and can be mass-produced in a cost-effective manner through continuous processes, over the conventional methods. The inventors have made an earnest study for improving mechanical properties relating to the rigidity and the strength of the three-dimensional cellular light structure, together with high efficiency, low cost and mass-productivity in weaving method, and finally accomplished the present invention.
[Disclosure]
[Technical Problem]
The present invention has been made to solve the above problems occurring in the prior art. It is an object of the invention to provide a Kagome truss-type three-dimensional light structure formed of six-axial continuous helical wire groups intercrossed at 60 degrees or 120 degrees in a space, wherein the three-dimensional light structure can be easily manufactured in a uniform pattern through continuous processes comprising a step of forming a plurality of two-dimensional Kagome planes consisting of 1st, 2nd and 3rd-axis helical wires and a step of assembling 4th, 5th and 6th-axis helical wires in out-of plane directions on two-dimensional Kagome planes consisted of the 1st, 2nd and 3rd-axis wires, and wherein close contact structure among the wires can be realized to thereby improve the mechanical properties such as strength, rigidity or the like. It is another object of the invention to provide a method of mass-producing the three-dimensional light structure in a cost-effective manner.
The three-dimensional light structure according to the present invention is manufactured in such a manner that a continuous wire is directly woven into a three-dimensional structure, not in the manner that planar wire-nets are simply laminated and bonded. Therefore, the cellular light structure of the invention is very similar to the ideal Kagome truss, and thus exhibits a good mechanical and electrical property.
[Technical Solution]
The features of the present invention for attaining the aforementioned objects are as follows.
(1) A three-dimensional cellular light structure manufactured by assembling 1st, 2nd, 3rd, 4th, 5th and 6th-axis wires in three-dimensional space, wherein the 1st, 2nd, 3rd, 4th, 5th and 6th-axis wires have a helical shape, and wherein the 1st, 2nd and 3rd-axis wires are assembled to form a plurality of two-dimensional Kagome planes and the 4th, 5th and 6th-axis wires are assembled in out-of plane directions on two-dimensional Kagome planes consisted of the 1st, 2nd and 3rd-axis wires.
(2) The three-dimensional cellular light structure, wherein the 1st, 2nd and 3rd-axis wires are assembled to form the two-dimensional Kagome planes of A, B and C layers in sequence from the bottom, and the wires in one layer are arranged to be constantly shifted from the wires on adjacent layers so as to maintain position deviations in horizontal and vertical directions with respect to the adjacent layers.
(3) The three-dimensional cellular light structure, wherein the wires in each layer are arranged to maintain a horizontal deviation lx and a vertical deviation ly between two adjacent layers, and the wires in each layer form the two-dimensional Kagome planes.
(4) The three-dimensional cellular light structure, wherein the two-dimensional Kagome planes of the A, B and C layers are repeatedly laminated in a manner of A, B, C, A, B, C, . . . , while maintaining prescribed distance between two adjacent layers.
(5) A method of manufacturing a three-dimensional cellular light structure, the method comprising:
a helical wire forming step of forming 1st, 2nd, 3rd, 4th, 5th and 6th-axis helical wires;
a two-dimensional Kagome plane forming step of forming a plurality of two-dimensional Kagome planes by assembling the 1st, 2nd and 3rd-axis helical wires on frames of a frame assembly;
a frame laminating step of connecting and laminating the frames by means of connection support rods; and
a step of fabricating a three-dimensional cellular light structure by assembling the 4th, 5th and 6th-axis helical wires into the 1st, 2nd, and 3rd-axis helical wires in each frame.
[Advantageous Effects]
According to the present invention relating to a three-dimensional cellular light structure and a method of manufacturing the same, the 1st, 2nd and 3rd helical wires are assembled on frames to form a plurality of two-dimensional Kagome planes, the 4th, 5th and 6th wires are assembled with the wires in the two-dimensional Kagome planes to form the three-dimensional cellular light structure. Therefore, the three-dimensional cellular light structure consisting of continuous wires can be easily manufactured, thereby enabling a mass production and cost-down.
In addition, since the continuous wires of the three-dimensional cellular light structure of the present invention have a helical shape, the three dimensional cellular light structure can be assembled by rotating insertion of the helical-shaped wires and also close contacts between the wires are enhanced without causing any damage to the intended truss structure. Accordingly, desired mechanical properties can be ensured even if the three-dimensional cellular light structure is not further subject to post-processing such as welding, brazing, soldering, liquid, or the like.